feat: Enhance ID mapping service robustness, add defensive guards, and expand migration engine and API testing.

backend/src/core/superset_client.py

@@ -400,6 +400,8 @@ class SupersetClient:
     # @RETURN: Dict - Ответ API в случае успеха.
     def import_dashboard(self, file_name: Union[str, Path], dash_id: Optional[int] = None, dash_slug: Optional[str] = None) -> Dict:
         with belief_scope("import_dashboard"):
+            if file_name is None:
+                raise ValueError("file_name cannot be None")
             file_path = str(file_name)
             self._validate_import_file(file_path)
             try: